1. Field of the Invention
This invention relates to the field of paint-stripping compositions.
2. Description of the Prior Art
The present invention relates generally to improved compositions for paint stripping. For a number of years methylene chloride was the principal component of paint stripping compositions because of its effectiveness in quickly softening most types of paints. For a number of reasons, however, the use of methylene chloride has become disfavored. Evidence of its toxicity to humans and the environment have caused some to seek alternative formulations.
A number of compounds have been offered as substitutes for methylene chloride. Among the principal compounds that have found to be effective to one degree or another in paint stripping formulations are N-methyl-2-pyrrolidone (NMP), gamma-butyrolactone (BLAC), tetrahydrofurfuryl alcohol (THFA), and furfuryl alcohol (FA). It has also been found that the efficacy of these compounds as paint removers can be improved by using them in combination with one another or with other compounds. For example, FA and THFA have been used in combination (U.S. Pat. No. 4,600,522). U.S. Pat. No. 4,366,002 teaches the use of two of FA, THFA, and a substituted alcohol of FA or THFA.
Oxygenated aliphatic solvents (e.g., glycols, ethers, esters, alcohols, and organic acids) are among the most frequently found additives used in conjunction with the aforementioned compounds. For example, FA has been used in combination with ethoxytriglycol and ethylene glycol phenyl ether (U.S. Pat. No. 3,551,340); NMP and BLAC in combination with ethyl 3-ethoxypropionate (U.S. Pat. No. 5,098,592); NMP in combination with an oxygenated aliphatic solvents (preferably one of the lower alkyl esters of 3-ethoxypropionate, e.g., ethyl 3-ethoxypropionate), wherein THFA may be substituted for part or all of oxygenated aliphatic solvent (U.S. Pat. No. 5,049,314); and NMP and THFA in combination with a variety of ethers, ketones, alcohols, esters (U.S. Pat. Nos. 4,274,884 and 4,664,721).
Other additives have also been suggested. Amines have been used as accelerators in conjunction with ethoxylated FA, ethoxylated THFA, and NMP (U.S. Pat. No. 4,737,195). Aromatic hydrocarbons (U.S. Pat. No. 4,128,810) and aliphatic hydrocarbons (U.S. Pat. No. 5,015,410) have been used in conjunction with NMP; and organic acids have been used with NMP and BLAC (U.S. Pat. No. 5,035,829). Still others have attempted a two phase system employing glycol phenyl ether, ethoxylated FA, and combinations thereof in an organic phase dispersed in an aqueous phase (U.S. Pat. No. 4,619,706).
Many formulations employing alternatives to methylene chloride suffer from a variety of disadvantages. Those using THFA are preferably used at elevated temperatures on the order of 200.degree. F. because they act too slowly at ambient temperatures. Others are intended for use in baths, where the object to be stripped must be immersed in the bath. Those requiring the use of NMP are expensive due to the relatively high cost of NMP. Furthermore, NMP is derived from non-renewable petroleum sources. Aliphatic dibasic ester based products are too slow and not effective enough. Consequently, it has been desirable to develop an effective paint stripping composition that circumvents these disadvantages without reintroducing the disadvantages posed by methylene chloride paint stripping technology.